MailTwin vs Grammarly for email: polishing your words, or writing them?

This comparison is less "either/or" than the others, because the two tools do different jobs. Grammarly is a writing checker and rewriter that follows you across nearly everything you type — it makes what you wrote clearer, more correct, better-toned. MailTwin is an email author: you select a message in Apple Mail, tell it what you want to say, and it writes the full reply in your own learned voice.

The practical question for a Mac user with an inbox: which problem do you actually have? If your drafts exist but need polish, that's Grammarly's job. If the drafts don't exist yet — if the tab you're avoiding is the writing — that's MailTwin's. Some people legitimately want both.

At a glance

Correction vs. authorship

Grammarly's strength is breadth and refinement. It catches grammar and spelling, tightens wording, adjusts tone, and offers full-sentence rewrites — across your browser, your documents, and your email client. For anyone writing English as a second language, or writing high-stakes prose all day, it's a mature, best-in-class tool. In 2025 it acquired Superhuman and now anchors a whole productivity suite.

But Grammarly starts after you've written something. The blank reply box is still yours.

MailTwin starts before. Select the email, type a few keywords — can't friday, propose tuesday, ask about invoice — and it drafts the complete, polite reply saying exactly that, in the voice it learned from your own sent mail. You decide what to say; MailTwin says it, and you review before anything sends. Christopher reports that this workflow saves him an hour or more on busy email days; individual results vary.

Whose voice comes out

Grammarly's tone tools adjust text toward targets: friendlier, more formal, more confident. Useful — but the underlying register is Grammarly's idea of good writing.

MailTwin's voice layer is built from you: it indexes your sent mail locally (explicit-only — you start it; 200 messages per account by default) and builds a separate style profile per account. Your work replies sound like your work self; your personal replies sound like your personal self; switching mailbox switches voice automatically. And because generated email carries real risk, every MailTwin rewrite passes an on-Mac validator — changed numbers, dates, or links and invented sign-offs are rejected before they reach your draft.

Cost and where your words go

Grammarly Pro runs $12 per month billed annually — $144 a year, every year — with monthly AI prompt quotas (2,000/month on Pro as of July 2026). Its free tier is genuinely useful for basic checking. Text you write is processed in Grammarly's cloud; that's inherent to how it works, and the company documents its practices.

MailTwin is $19.90 once, with lifetime 1.x updates and a 30-day full trial. There's no MailTwin server in the path at all: content goes directly from your Mac to the AI provider you chose, or stays on the Mac entirely with Apple Intelligence (macOS 26+) or Ollama — both free. Cloud keys bill at provider rates with a live cost log in Settings.

Choose Grammarly if…

• You write a lot outside email — reports, docs, posts, chat — and want one assistant everywhere. MailTwin only works in Apple Mail, on macOS.
• English isn't your first language and you want continuous correctness and fluency coaching, which is Grammarly's home turf.
• You need plagiarism or AI-text detection, team style guides, or brand tones.
• Your writing exists and needs refinement more than generation.

Choose MailTwin if…

• Email is the bottleneck: you know what to say and resent typing it. Keyword-to-full-reply in your own voice is the core of the product.
• You want per-account voice — work and personal each in their own register — learned locally, never in the background.
• You want to pick your AI engine (or pay nothing, on-device) rather than use one vendor's cloud with prompt quotas.
• One-time pricing appeals: $19.90 once vs. $144/year. Full disclosure of our trade-offs: Apple Mail only, macOS only, no mobile app, bring-your-own-key for cloud engines (two engines need none), and it's a v1 product.

Can you use both?

Yes, and it's a sensible pairing: MailTwin drafts the reply in your voice inside Apple Mail; if you also run Grammarly's Mac app, it can check whatever ends up in your compose window like any other text (as of mid-2026). Polish plus authorship don't conflict.

FAQ

Is MailTwin a Grammarly alternative?

Only partially. Grammarly checks and improves writing everywhere; MailTwin writes Apple Mail replies for you, in your learned voice. They overlap on email polish (MailTwin's Improve draft) but solve different core problems.

How much does Grammarly cost in 2026?

As of July 2026: a free tier with about 100 AI prompts per month, and Pro at $12/month billed annually ($30 month-to-month). MailTwin is $19.90 one-time.

Does Grammarly write emails in my personal style?

Grammarly adjusts tone and offers rewrites toward general targets. MailTwin builds a style profile from your own sent mail, per account, and drafts new replies in that voice.

Does MailTwin check grammar?

Its Improve draft action rewrites and tightens your draft with your chosen AI engine, protected by a validator that keeps numbers, dates, links, and sign-offs intact. It isn't a persistent cross-app checker like Grammarly.

Is my email content safe with each?

Grammarly processes text in its cloud. MailTwin routes content directly from your Mac to the provider you chose — or keeps it fully on-device — with no MailTwin server involved, ever.

Try the authorship side free

If the blank reply box is the real problem, test the fix on your own inbox. 30-day full trial, no card, then $19.90 once.

Download MailTwin →